Regular voyages to the Mexican Riviera, long a mainstay of San Diego’s cruise ship business, are likely to end by the fall of 2012 with the decision by Holland America to move one of its key liners to Australia.

The cruise line’s 1,926-passenger Oosterdam and the 2,500-passenger Carnival Spirit are the only two vessels that currently head to the Mexican Riviera on a regular basis, and both are now scheduled to leave San Diego after April of 2012. The Spirit as well will be relocated to Australia.

While the fall 2012-2013 schedules for the cruise lines have yet to be finalized, Port of San Diego official Rita Vandergaw acknowledged that for now it appears that San Diego will no longer have regular cruises to the Riviera.

The redeployment of the Oosterdam, which makes seven-day cruises to Mexico, marks the third ship to leave San Diego waters in the wake of a prolonged economic downturn and rising violence in Mexico. The net effect has been a plunge in cruise ship calls, which are an important component of San Diego’s tourism economy.

“I’m not going to get discouraged until I get a final word, but obviously the whole Mexican Riviera situation is very discouraging,” said Vandergaw, the port’s marketing director. “It’s very fluid but I’m the eternal optimist.”

Holland America declined to comment Friday on why it had decided to pull the Oosterdam out of San Diego. The cruise line pointed out that it has yet to release its Mexico deployment for the fall of 2012, although it had recently announced that the Oosterdam would no longer be in San Diego because the ship is headed to the South Pacific.

“This year we are operating more than 60 cruises from San Diego and we will continue to sail Hawaii, Mexico, South Pacific and Panama Canal itineraries from the San Diego gateway,” the cruise line said in a statement. “The city and the port have been wonderful for us and our operations and we expect that relationship will continue.”

The loss of both the Carnival and Holland America ships represents a huge economic blow to the region, depriving the area of more than $100 million in spending annually. The Port of San Diego estimates that each ship beginning and ending a cruise in the port contributes an estimated $2 million to the local economy. Each of the two vessels makes roughly 26 trips to the Riviera from San Diego between October and April.

The news of the Oosterdam’s planned departure comes on the heels of the San Diego Port’s recent completion of a new $28 million cruise ship terminal at the Broadway Pier that was designed to accommodate overflow business from its larger terminal at B Street.

At its peak in 2008, the Port of San Diego saw 255 ships dock at the Embarcadero, but that number is expected to fall to 103 this year and was forecast to be as few as 76 by 2013 before the announcement by Holland America, according to the Port. Vandergaw noted that once a cruise line leaves, it typically takes 18 months to make a decision on a new deployment, which means that San Diego may not see a return of its lost cruise ship business until as late as 2015, she said.

Diminished interest in travel to Mexico because of continued violence there has persuaded the cruise lines to pull out of that region in favor of more desirable and profitable destinations like Australia. Several of the ships also no longer make stops in Mazatlan because of recent attacks there.

The exodus from Mexico began last year, when Carnival Cruise Lines relocated San Diego’s only year-round ship, the Elation, to Mobile, Ala.

“The problem is the perception of the unsafe experience in Mexico,” said Tom Dow, vice president for public affairs with Carnival Corp., the parent company of Carnival and Holland America. "And it’s more a problem on the Pacific Coast than the Atlantic Coast. Even though there have been only a few isolated incidents in Mexico that we don’t think are drug connected, it doesn’t take very much for people to make a decision to defer that trip and go someplace else.

While Holland America has the largest number of vessels coming in and out of San Diego, there are still eight other cruise lines, including Celebrity, Crystal and Princess, operating in San Diego, some much less frequently than others. Some of those ships are making longer voyages to Hawaii, Panama Canal and the Sea of Cortez.

Vandergaw pointed out that San Diego has attracted some new business for 2012, including eight more calls by Celebrity, but that still isn’t enough to blunt the impact of so many ship departures.

“Yes, it feels like we’re pushing the rock up the hill, and yes, we were at our peak of 300 cruise calls and now down to 103 and dropping even more for 2012,” Vandergaw said. “But while we’ve lost business, we still have a robust cruise business, and we’re working very hard to get in other service but the Mexico situation is daunting.

Although cruises to the Mexican Riviera have long offered an inexpensive, convenient vacation option for San Diegans, it’s unlikely they’ll be missed by cruise aficionados, said travel agent Linda Rigg of Carefree Vacations. Many of her customers, she said, have taken the Mexican voyages repeatedly, but have since tired of the sameness of the itineraries and are looking for more exotic destinations, she said.